20644821 has 8 divisors (see below), whose sum is σ = 30584960. Its totient is φ = 13763196.

The previous prime is 20644807. The next prime is 20644831. The reversal of 20644821 is 12844602.

It is not a de Polignac number, because 20644821 - 2⁷ = 20644693 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 764623 = 20644821 / (2 + 0 + 6 + 4 + 4 + 8 + 2 + 1).

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20644831) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 382285 + ... + 382338.

It is an arithmetic number, because the mean of its divisors is an integer number (3823120).

Almost surely, 2^20644821 is an apocalyptic number.

It is an amenable number.

20644821 is a deficient number, since it is larger than the sum of its proper divisors (9940139).

20644821 is an equidigital number, since it uses as much as digits as its factorization.

20644821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 764632 (or 764626 counting only the distinct ones).

The product of its (nonzero) digits is 3072, while the sum is 27.

The square root of 20644821 is about 4543.6572273885. The cubic root of 20644821 is about 274.3281494752.

The spelling of 20644821 in words is "twenty million, six hundred forty-four thousand, eight hundred twenty-one".